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Optimizing the Manufacture of Orthopedic Devices

By Aaron Bailey, Director of Sales - Medical, NN Inc., PEP | May 17, 2017

Electron beam welding offers a beneficial process for joining dissimilar materials and targeting very specific locations.

Strength and efficacy is critical in medical devices. For this reason, electron beam (EB) welding is an ideal process for many types of complex orthopedic instruments because the technology produces an ultra-strong weld with a small heat-affected zone (Figure 1).
 
By penetrating deep into a metal, unlike typical surface welding, metal components are fused via high velocity electrons that travel throughout the mating area, deep into the parts while protecting surrounding materials from heat exposure. This is particularly beneficial for orthopedic instruments, which often require strong, deep welds.
 
What Is Electron Beam Welding?
When an application requires a very precise, clean weld but a small heat affected zone (HAZ), electron beam welding can be an ideal alternative to conventional welding. Electron beam welding—which originated from applications in the aerospace industry—penetrates deep into a metal unlike typical surface welding [e.g., gas tungsten arc or tungsten inert gas (TIG) welding, or laser beam welding].


Figure 1: Using a targeted, high-velocity electron beam, even the smallest medical device components can be welded with extremely high precision and strength.
EB welding is a unique process whereby metal components are fused via high-velocity electrons that can travel throughout the mating area, deep into the parts. It is conducted in a vacuum environment to melt the material without the presence of gas molecules. The electron beam is focused using magnetic fields and applied to the targeted materials to be joined. It can be aimed into a blind hole or below the surface of mating components and offer high depth-to-width ratios. Welds can go deep and only affect a narrow sliver of the surface, protecting surrounding materials from heat exposure. This means, for example, that a plastic handle can be assembled or over-molded prior to welding, reducing assembly time and potentially lowering the overall cost of the device.
 
During EB welding, fixtures are used to secure the medical device components during the process. To achieve optimal production rates, multiple parts can often be welded during a single vacuum cycle. The fixtures are then attached to the welder’s CNC table, where they will be shifted into precise position under the electron beam at the appropriate time.
 
The vacuum chamber is secured and the air is either partially or completely pumped out, depending on the custom specifications of the particular job. Factors such as beam alignment and focus, power, and weld penetration may be checked and adjusted during a test run. When satisfied that the parameters are correct, the operator then initiates the CNC table programming, the electron beam is fired up, and the welding process occurs. Upon completion of the welding cycle, the vacuum chamber is pumped down and the parts are ready for removal and inspection.
 
The Benefits of Electron Beam Welding
Electron beam welds are extremely strong and precise and the process is very repeatable, allowing manufacturers to achieve consistently accurate results every time. Because it is performed in a vacuum, there is low risk of contamination. By using a highly targeted electron beam, it provides superior depth of penetration and high depth-to-width ratio.
 
EB welding is conducive to joining dissimilar materials that would otherwise be unable to be joined with other welding methods due to differences in melting points.
 
Additionally—and of particular importance for medical device components—the autogenous welding process ensures that the biocompatibility of selected materials is not changed during welding. 
 
Electron Beam Welding for Orthopedic Instruments
Electron beam welding is becoming a sought after manufacturing approach for many types of advanced orthopedic implants that meet surgical challenges thanks to ultra-strong welds and high depth-to-width ratios.
 
Since electron beams can be aimed with exceptional accuracy, even the smallest medical device components can be successfully welded with extremely high precision and strength. EB welding can allow entire assemblies to be completed in one weld cycle and even supports complex stainless steel assemblies, which won’t oxidize in the body over time.
 
An example of electron beam welding being used for an orthopedic device is an assembly that had to be made as a two-piece construction (Figures 2 and 3). It would be very difficult to TIG around the Ø0.098 inch rod, so an e-beam burn down lip was added to the mating component (for cosmetic reasons) and then the parameters for the power levels were dialed in to ensure a consistent weld through the assembly welding of each part. The burn down lip area can then be easily finished to create a seamless weld.


Figures 2 (above) and 3 (below): E-beam weld assembly diagram


Conclusion
With electron beam welding, metal components are fused via high-velocity electrons that travel throughout the mating area, penetrating deep into the metal parts without heating the surrounding areas. Electron beams can be aimed with exceptional accuracy to precisely weld even the smallest medical device components or complex assemblies.
 
Electron beam welding drastically expands where welds can be created and improves the strength and quality of those welds. Its precise, high-strength nature is well-suited for durable, biocompatible metal instruments that are used in challenging intraoperative environments. This is particularly beneficial for orthopedic devices.

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